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Documentation of the Evaluation of CALPUFF and Other Long ...

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<strong>the</strong> fitted Gaussian plume is not a very good fit <strong>of</strong> <strong>the</strong> observations <strong>and</strong> <strong>the</strong> Cmax parameter is<br />

not a good indicator <strong>of</strong> model performance. Comparison <strong>of</strong> <strong>the</strong> predicted <strong>and</strong> observed Omax<br />

values that represents <strong>the</strong> maximum observed concentration across <strong>the</strong> monitoring sites <strong>and</strong><br />

<strong>the</strong> maximum predicted value at any <strong>of</strong> <strong>the</strong> 200 receptors along <strong>the</strong> arc is an apple‐orange<br />

comparison. We would expect <strong>the</strong> predicted Omax value to be <strong>the</strong> same or larger than <strong>the</strong><br />

observed Omax value given <strong>the</strong>re are ~5 times more samples <strong>of</strong> <strong>the</strong> plume in <strong>the</strong> model<br />

predictions compared to <strong>the</strong> observations. This is <strong>the</strong> case for all <strong>of</strong> <strong>the</strong> <strong>CALPUFF</strong>/MMIF<br />

sensitivity tests. However, when <strong>CALPUFF</strong> is run using CALMET with no MM5 data (BASE), <strong>the</strong><br />

predicted Omax value is less than <strong>the</strong> observed value for both <strong>CALPUFF</strong> V4.0 <strong>and</strong> <strong>CALPUFF</strong> V5.8,<br />

which is an undesirable attribute.<br />

The fitted plume width (sigma‐y) based on observations is almost doubled <strong>the</strong> fitted plume<br />

width based on <strong>the</strong> <strong>CALPUFF</strong> model predictions for all <strong>the</strong> <strong>CALPUFF</strong> simulations. However, this<br />

is likely due in part to <strong>the</strong> poor Gaussian plume fit <strong>of</strong> <strong>the</strong> observations. Figure 4‐2 is reproduced<br />

from <strong>the</strong> 1998 EPA <strong>CALPUFF</strong> tracer test report <strong>and</strong> compares <strong>the</strong> <strong>CALPUFF</strong> fitted Gaussian<br />

plume concentrations with <strong>the</strong> 13 observed tracer concentrations, where <strong>the</strong> predicted <strong>and</strong><br />

observed tracer distributions have been rotated so that <strong>the</strong>ir centerlines match up. Of <strong>the</strong> 13<br />

monitors pictured along <strong>the</strong> 100 km arc, four have substantial (> 2.0 ppt) concentrations<br />

whereas <strong>the</strong> tracer concentrations at <strong>the</strong> remaining monitoring sites are mostly

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